1. Field of the Invention
The present invention relates to an on-demand system having a plurality of terminals and one center device which has a plurality of on-demand servers and, more particularly, to an on-demand system characterized in a control system of power-on/off (power application/removal) of an on-demand server.
2. Description of the Related Art
Typical of an on-demand system having a plurality of terminals and one center device which has a plurality of on-demand servers is a video-on-demand (VOD) system. In the field of this system, each of a plurality of terminals is generally called a set top box (STB). While supplied with terminal source power, each STB is in an operative condition, where it is allowed to transmit a request signal for requesting for video-on-demand services to the center device.
Each of a plurality of video-on-demand servers (VOD servers) of a center device is in operation when supplied with server source power. The center device has a request control unit. Upon receiving a request signal from one of the plurality of STBs, this request control unit transmits a data delivery request signal of delivery data according to the request signal to one of the VOD servers in operation to cause the one VOD server to deliver delivery data to the STB which has transmitted the request signal.
One of on-demand systems is disclosed, for example, in Japanese Patent Laying-Open No. 7-327221. Japanese Patent Laying-Open No. 7-327221 recites a technique of sending out a halt signal or a halt release signal from an STB to a center send-out device which controls reproduction and stoppage of a VOD server to halt a program being reproduced or resume reproduction of the same and a technique of an STB having a halt time monitoring timer and a power-off monitoring circuit, which enable displaying of alarm indications on a screen of the STB when a halt time exceeds a predetermined time or when the power of the STB is to be turned off during halt.
In conventional on-demand systems such as a VOD system, it is a common practice that all the VOD servers are in operation at any time irrespective of the number of STBs in operation. In addition, power supply control of a VOD server is conducted manually.
It is therefore impossible to automatically control power-on/off (power application/removal) of a VOD server according to the number of STBs in operation, which causes a waste on operations management and operation costs.
First object of the present invention is to provide an on-demand system capable of automatically controlling power-on/off (application/removal) of on-demand servers according to the number of terminals in operation.
A second object of the present invention is to provide an on-demand system facilitating operations management of on-demand servers, as well as enabling reduction of operation costs, and also enabling improvement in reliability of on-demand servers with ease.
According to one aspect of the invention, an on-demand system including a plurality of terminals and one center device, the center device including a plurality of on-demand servers and a request control unit, the request control unit, in response to a request for on-demand services from the terminal, causing one of the on-demand servers in operation to deliver delivery data according to the request to the one of the plurality of terminals which has made the request, wherein
the center device comprises a power control unit for controlling power-on/off of the on-demand servers according to the number of the terminals in operation,
the power control unit comprises
count means which counts up in response to an on signal transmitted from the terminal which has started operation and counts down in response to an off signal transmitted from the terminal which has stopped operation, and
power control means having a threshold value corresponding to the number of the terminals in operation and the necessary number of the on-demand servers for comparing the count value and the threshold value to supply power to the on-demand server to be newly operated and stop power supply to the on-demand server whose operation is to be stopped.
In the preferred construction, each of the plurality of terminals includes signal transmission means for transmitting the on signal to the center device when supply of source power to the terminal is started and transmitting the off signal to the center device when supply of the source power is stopped.
In another preferred construction, when the count value reaches the threshold value, the power control means sends out a power supply signal for supplying source power to the on-demand server to be newly operated and when the count value falls below the threshold value, sends out a power supply stop signal for stopping supply of source power to the on-demand server whose operation is to be stopped.
In another preferred construction, the center device comprises a file device connected to the plurality of on-demand servers for storing accumulated data as file data, and
upon reception of the data delivery request from the request control unit, one of the on-demand servers in operation finds the delivery data according to the request from among the file data stored in the file device and delivers the delivery data to the terminal which has made a request.
In another preferred construction, before the count value reaches the threshold value, the power control means sends out a notification signal which notifies the request control unit of the on-demand server in currently operation and when the count value reaches the threshold value to newly operate the on-demand server, sends out a notification signal which notifies the request control unit of all of the on-demand servers including the newly operated on-demand server.
In another preferred construction, when the count value falls below the threshold value to stop operation of the on-demand server, the power control means sends out, to the request control unit, an instruction signal for inhibiting transmission of the data delivery request to the on-demand server whose operation is stopped.
In another preferred construction, when the count value falls below the threshold value, the power control means sends out, to the request control unit, an instruction signal for inhibiting transmission of the data delivery request to the on-demand server whose operation is to be stopped,
the request control unit, upon reception of a processing completion signal indicating that delivery of the delivery data in responses to all the requests is completed from the on-demand server whose operation is to be stopped, sends out, to the power control means, a power-off permission signal which permits stoppage of supply of source power to the on-demand server whose operation is to be stopped, and
the power control means, upon reception of the power-off permission signal, sends out a power supply stop signal for stopping supply of source power to the on-demand server whose operation is to be stopped.
In another preferred construction, the power control means
has, as the threshold value, a plurality of values based on an allowable capacity per one the on-demand server for the terminals and the necessary number of the on-demand servers for handling the number of the terminals currently in operation,
first sets a threshold value meeting the number of the terminals in operation and the number of on-demand servers in operation corresponding to the terminals,
when the count means counts up a count value, compares the threshold value set and the count value and when the count value reaches the threshold value, sends out a power supply signal for supplying source power to the on-demand server to be newly operated, as well as newly setting the threshold value, and
when the count means counts down a count value, compares a threshold value obtained for the case where the number of necessary on-demand servers is reduced by one with the count value and when the count value falls below the threshold value, sends out a power supply stop signal for stopping supply of source power to the on-demand server whose operation is to be stopped, as well as setting the threshold value to be the threshold value obtained for the case where the necessary number of on-demand servers is reduced by one.
In another preferred construction, as the threshold value, a value is set which is obtained by multiplying a value obtained by subtracting a certain value from an allowable capacity per one the on-demand server for the terminals for leaving a margin by the number of on-demand servers necessary for handling the number of the terminals in operation.
In another preferred construction, the power control means
has, as the threshold value, a plurality of values based on an allowable capacity per one the on-demand server for the terminals and the necessary number of the on-demand servers for handling the number of the terminals currently in operation,
first sets a threshold value meeting the number of the terminals in operation and the number of on-demand servers in operation corresponding to the terminals,
when the count means counts up a count value, compares the threshold value set and the count value and when the count value reaches the threshold value, sends out a power supply signal for supplying source power to the on-demand server to be newly operated, as well as newly setting the threshold value, and
when the count means counts down a count value, compares a threshold value obtained for the case where the number of necessary on-demand servers is reduced by one with the count value and when the count value falls below the threshold value, sends out, to the request control unit, an instruction signal for inhibiting transmission of the data delivery request to the on-demand server whose operation is to be stopped,
the request control unit, upon reception of a processing completion signal indicating that delivery of the delivery data in response to all the requests is completed from the on-demand server whose operation is to be stopped, sends out, to the power control means, a power-off permission signal which permits stoppage of supply of source power to the on-demand server whose operation is to be stopped, and
the power control means, upon reception of the power-off permission signal, sends out a power supply stop signal for stopping supply of source power to the on-demand server whose operation is to be stopped, as well as setting the threshold value to be a threshold value obtained for the case where the necessary number of on-demand servers is reduced by one.
Also, as the threshold value, a value is set which is obtained by multiplying a value obtained by subtracting a certain value from an allowable capacity per one the on-demand server for the terminals for leaving a margin by the number of on-demand servers necessary for handling the number of the terminals in operation.
Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow.